A randomised controlled effectiveness pilot trial of the Incredible Years Parents and Babies Program (IY baby)offered as a universal intervention in two municipalities in Denmark. 120 families will be randomised to IY Baby (intervention) og Usual Care (UC- control). Families recruited to the study have infants aged 0-4 months old. All first time mothers in one municipality and all mothers in another municipality are recruited. Outcomes are measured at 20 weeks post baseline and when the child is 18 months old. The aim of this trial is to estimate the effectiveness of the IY Baby program on parent and infant well-being, development and relationship and establish parameters for a definitive trial. In addition, the pilot study will also gather information on parent recruitment and participation to inform future research in this area.